Deflect arrows is a feat, with both prerequisites and usage requirements (hand free) which only works for attacks directed at yourself.
You cannot ready an action to "When the archer shoots his bow, I want to move in front of him, and grab the arrow out of the air." Even if you have the deflect or snatch arrows feats, the attack wasn't aimed at you, so you can't deflect/snatch the arrow.
Ready action move is fine. Ready action move and do something else is not. You can only ready a standard, move, swift, or free action. You can also take a 5' step as part of it. You cannot ready a move and standard action.
At best, the character could provide soft cover to the origin point the spellcaster is targeting by moving in the way. The spellcaster then would have to make a ranged touch attack against the grid intersection. AC 5 + soft cover + 4 = AC 9. If the spellcaster happened to have improved precise shot, that would drop back to AC 5.
What about a Kasatha Bow Nomad? Their version of deflect arrows allows them to deflect any ranged attack within 30ft of them, without rolling. which moves the question in this one, very limited, instance to is a fireball considered a ranged attack? If so Kasathans just became ridiculous.